The present invention relates to a method for driving plasma display panels (PDP) which are used as display terminals for television sets and computers.
A plasma display panel (referred to as xe2x80x9cPDPxe2x80x9d hereinafter) is a device which displays letters or pictures by using light emitted from plasma generated during gaseous discharge. The PDP is classified into a DC-type and an AC-type depending on a driving method for providing an electric field thereto in order to make the plasma.
Since the PDP has advantageous characteristics such as large screen size of more than 40 inches, ability to display full-color images and wide viewing angle compared with other flat panel devices, it results in a rapid increase in its application area such as next generation high definition televisions (HDTV) capable of hanging on the wall and a multimedia display apparatus combining a TV and a personal computer.
There are several methods for driving the AC-type PDP. One of the methods is disclosed in U.S. Pat. No. 5,541,618, assigned to Fujitsu Limited. An Address Display period Separated (ADS) sub-field method is disclosed and used for driving the PDP in this patent. In accordance with this patent, one image frame is divided into n number of subframes. Each of the subframes includes: an addressing period subsequently providing scan pulses to all scan electrodes in order to indicate cells to be lit; and a display period having a predetermined sustain pulses and concurrently applying sustain pulses to all the scan electrodes, wherein a number of the sustain pulses is predetermined differently for each subframe. The scan pulses are continuously provided onto all the scan electrodes and address pulses are applied onto data electrodes in response to picture data to be displayed. However, according to the ADS sub-field method, since every subframe should have an addressing period for addressing all the scan lines, the display period is relatively shortened. Therefore, the brightness of an image may be decreased.
In order to prevent users from seeing flickers on the screen, the time for controlling illumination of one frame should be limited to about {fraction (1/60)} sec or less, namely 16.67 ms. In the NTSC system having 480 scan lines, if one image frame is divided into 8 number of subframes, it takes about 11 to 12 ms in addressing one image frame. Because the remaining time for the display period which TV viewer can substantially recognize the image is only 5 to 6 ms, the efficiency becomes only 30% and the brightness of the image is reduced. However, if increasing frequency of sustain pulse in order to compensate the brightness reduction, power consumption is increased and reliability of driving is also decreased.
In the case of HDTV having 1024 scan lines, because it takes about 24 to 25 ms in addressing one image frame, there is not enough remaining time for the display period. As a result, the TV viewer cannot recognize the image. Also, since pixels corresponding to scan electrodes are continuously selected for an addressing period, the reliability of driving is reduced by a result of static delay effect, which occurs in discharge firing.
One specific driving method for ADS is disclosed in EP patent No. 0,965,975A1 xe2x80x9cMethod and apparatus for driving plasma display panelxe2x80x9d. A plasma display panel using this method has a plurality of first electrodes and second electrodes arranged parallel to each other, a plurality of third electrodes arranged to cross the first and second electrodes, and discharge cells defined within the areas in which the third electrodes cross the first and second electrodes. The electrodes are thus mutually arranged in the form of a matrix. According to a driving method for such a plasma display panel, a reset period is a period during which the distribution of wall charges in the plurality of discharge cells is uniformed. An addressing period is a period during which wall charges are produced in the discharge cells according to display data. A sustain discharge period is a period during which sustain discharge is induced in the discharge cells in which wall charges are produced during the addressing period. The driving method comprises a step of applying a first pulse as shown in prior art FIG. 3 (xe2x88x92Vwx, Vwy) in which an applied voltage varies with time so as to induce first discharge in the lines defined by the first and second electrodes, and a step of applying a second pulse (Vex, xe2x88x92Vey) in which an applied voltage varies with time so as to induce second discharge as erase discharge in the lines defined by the first and second electrodes. These steps are carried out during the reset period.
FIG. 1 is a schematic diagram showing the structure of a surface discharge type PDP. FIG. 2 is a waveform diagram illustrating an ADS driving method implemented in the PDP shown in FIG. 1. During the addressing period, addressing discharge is induced by applying a scanning pulse successively to the Y electrodes. A voltage Vx is, conventionally applied to the X electrodes that are paired with the Y electrodes, to which the scanning pulse has been applied, to define display lines. Consequently, addressing discharge is induced. In contrast, a voltage xe2x88x92Vux is applied to X electrodes defining non-display lines. A potential difference from the Y electrodes is thus limited in order to prevent addressing discharge from being induced in the non-display lines. The scanning pulse is applied successively to the odd-numbered Y electrodes in order to induce addressing discharge. Thereafter, the scanning pulse is applied successively to the even-numbered Y electrodes in order to induce addressing discharge. This procedure is the same as that in the conventional method and is commonly referred to as a selective write method.
A second specific driving method for ADS is disclosed in U.S. Pat. No. 6,020,687 wherein a method for driving a plasma display panel includes carrying out an erase address operation when a display on the screen is renewed. The erase address operation includes the steps of carrying out an address preparation operation for producing the wall charge in all the discharge cells through a first step of generating a discharge only in a discharge cell in an ON-state, and a second step of generating a discharge only in a discharge cell in an OFF-state, and carrying out an operation for selectively erasing the wall charge in a discharge cell other than a discharge cell corresponding to data of the image to be displayed. FIG. 3 shows exemplary waveforms for voltage pulses applied to the electrodes by this erase address method. The pulse for the erase address discharge (a voltage pulse synthesized from an address pulse applied to the address electrode and a scan pulse applied to the scan electrode) is applied to create an address discharge only in non-selected cells to remove the stored wall charge. Accordingly, the sustain discharge does not occur later in these cells. This method is commonly referred to as the selective erase method in the industry.
Another method for driving the PDP is Address While Display (AWD). There have been proposed many PDP driving methods that use the AWD method, such as in the article by Lim G. S. xe2x80x9cNew Driving Method for Improvement of Picture Quality in 40-inch AC PDPxe2x80x9d Asia Display 98 pp. 591-594. In that article they adapted the new driving method to improve the picture quality that is called Distributed-Address and Sustain (DAS) method. This technique is different from the current ADS method. The address period and display period is not separated so the problem which reduces the light-emitting time in traditional ADS method is solved.
FIG. 4 shows the driving waveforms and timing diagrams, which were applied to the DAS method. The DAS method has a poor contrast ratio because the addressing method used is a non-selective write pulse followed by a selective erase pulse. Both pulses produce light output that is not part of picture data, therefore, resulting in a poor contrast ratio. Also, the time for line scan addressing during a free time is reduced. This is caused by loss of addressing time during the sustain pulse period.
A second driving method using AWD is described in the article xe2x80x9cMultiple Addressing in Single Sustain Method: A New High Speed Driving Scheme for ac-PDPxe2x80x9d EuroDisplay ""99 pp. 73-76. This Multiple Addressing in Single Sustain (MASS) method is introduced as a new high speed addressing scheme for AC-PDP. Since the multiple lines are addressed in a single sustain period while the sustain voltage is applied, the wall charge accumulation time is longer than the write pulse period enabling the high speed addressing. The exponential ramp erase waveform possible with MASS driving is found very effective to increase the operating margin and improve the picture quality.
The driving pulse waveforms of MASS are shown in FIG. 5. A group of scan lines are addressed in a single discharge period, Ts. The setup period which consists of priming and reset discharge is put only once at the start of a frame field followed by the sustain pulses without separate addressing period as in ADS. The addressing takes place after the transition of sustain pulse voltage with the scan (Y) electrode voltage settled at lower sustain voltage level, Vsxe2x88x92. While the negative scan pulses of VW are applied to the selected scan lines at the addressing period TA, the positive addressing pulses of VA are synchronously applied to the addressing (or data) electrodes in correspondence with the image data. The scan lines selected during the same sustain period receive the erase pulse simultaneously as the subfield periods are same for these lines. Since the write discharge is triggered with the DC level of sustain voltage (Vs=Vs+xe2x88x92Vsxe2x88x92) applied between the X-Y electrodes of front plate, the wall charge formation process continues even after the write pulse until the next sustain pulse transition occurs.
One of the major problems the MASS driving method has is in the data drive. The data driver must be returned to ground during the sustain transitions, resulting in a higher duty cycle. Thus, the power dissipation in the device is increased. Also, VA applied to the data driver IC is twice that of other drive schemes.
In summary, the most commonly used drive method is address display separate (ADS), used by Fujitsu and others. ADS driving has been widely adopted for its simple architecture and low discharge failure rate. However, as the number of display rows increase to do higher resolution displays, such as in HDTV, ADS driving becomes less effective since the required increased addressing period that would be required for the increase in the number of rows would leave little of the frame period for sustain pulses. With less time for sustain pulses in a frame period the maximum brightness that the display can obtain is reduced. If the sustain pulse width is reduced to increase the number of sustain discharges to increase brightness then the luminous efficiency is reduced. Typically on lower resolutions displays (480 rows) ADS uses three fourths of the frame period for addressing and one fourth for sustain discharges to produce the light emissions. This limits the number of rows that can be scanned and addressed per frame. The small period of the frame time used for sustain discharge pulses allows for only a finite number of sustain pulses, therefore the brightness of the display is limited. A drawback of the address while display (AWD) method is that in this scheme during sustain transitions there is no addressing. Therefore, the number of rows scanned and addressed is limited. Also, having the sustain and addressing waveforms as one results in compromises in the address drive.
In all prior PDP driving methods, however, all sustain discharges between the X and Y electrodes are conducted at discretely different time periods from the time periods during which the PDP cells are being addressed. This is because, during the sustain discharges, a potential would be induced onto the addressing electrodes thereby causing faults and preventing accurate addressing.
An object of the present invention is to overcome the limitations of the two drive methods that are currently being used to drive plasma display panels.
The new drive method in accordance with the principles of the present invention is Address Display Together (ADT). This method overcomes the above limitations in plasma display panel drives. In this scheme, the PDP is divided into blocks which are driven by independent controlled drive electronics. In operation, in one block or display area the cells are addressed while, simultaneously, in the remaining blocks or display areas the cells are sustained creating discharges and producing light emissions. The scan and sustain (X and Y) electrodes in the sustain blocks are driven simultaneously at opposite phase and between low and high potentials with respect to one another. Accordingly, although sustain discharges are produced in the cells of the sustain blocks, substantially no electrical potential is induced on the address or data electrodes. This makes possible for one block to have addressing waveforms while the remainder of the blocks have conditioning waveforms or sustain discharge pulses producing light emissions. Therefore, during a frame period there is almost 100% address time. The time for sustain discharge pulses is increased by a minimum of three times when compared to that of the ADS method.
In one form thereof the present invention is directed to a method of driving a plasma display panel having a plurality of pairs of first and second electrodes arranged parallel with one another. Third electrodes are arranged generally orthogonal to the first and second electrodes. A plurality of cells are defined at cross points of the electrode pairs and third electrodes. Sustain discharges are provided in the cells by changing the electrical potential of the first and second electrodes with respect to one another. The method includes the steps of simultaneously driving the first and second electrodes of at least one pair between low and high electrical potentials with respect to one another, whereby sustain discharges are provided at one or more cells of the one pair and substantially no electrical potential is induced on the third electrodes.
In one form thereof the present invention is directed to a method of driving a plasma display panel having a plurality of pairs of first and second electrodes arranged parallel with one another. Third electrodes are arranged generally orthogonal to the first and second electrodes. A plurality of cells are defined at the cross points of the electrode pairs and the third electrodes. Sustain discharges are provided in the cells by changing the electrical potential of the first and second electrodes with respect to one another. The method includes the steps of simultaneously driving the first and second electrodes of at least one pair substantially at opposite phase and between low and high electrical potentials with respect to one another, whereby sustain discharges are provided at one or more cells of the one pair and substantially no electrical potential is induced on the third electrodes.
In one form thereof the present invention is directed to a method of driving plasma display panels having a plurality of pairs of first and second electrodes arranged parallel with one another. Third electrodes are arranged generally orthogonal to the first and second electrodes and a plurality of cells are defined at cross points of the electrode pairs and the third electrodes. Electrical potential is placed on the first or second electrodes for conditioning the cells for thereafter addressing with the third electrodes. The method includes the steps of conditioning cells of at least one pair by placing electrical potential on the first or second electrodes of the one pair and, while conditioning the cells of the one pair, placing an electrical potential on the third electrodes whereby address charges are placed on cells of another pair of electrodes.